Check out this webpage http://www.creativepursuits.net/kayaking.htm
for some dryland tips. Mandy is a kayak instructor and a very smooth paddler. I'm not sure if she's on to Betty Buzz yet, but hopefully she will chime in here soon. I would never have thought a dryland exercise would help with a roll till I saw this. Watch those little videos next to each exercise.
In my experience...9 times out of 10, when a roll fails it is because the person is picking their head up too early and it throws them back down. Also, if you can open your eyes while under water to make sure your paddle blade is in the right position, you might find that helps. You don't want your paddle blade vertically slicing through the water, or diving way beneath the water's surface, and sometimes you won't know this is happening unless you see it.